When Kurdish fighters overran Islamic State’s last stronghold in Syria, victory was declared over the jihadist group. But many of Islamic State’s fighters and their families have survived the collapse of the caliphate. What should become of them? And can we be sure that the defeat of Islamic State is also a defeat of its ideology? Andrew Mueller is joined by NPR’s Jane Arraf, former MI6 global counter-terror chief Richard Barrett CMG OBE and Aimen Dean, former al-Qaeda militant turned MI6 agent.